1. Field of the Invention
The present invention relates to an image observing apparatus suited to a head mounted display (HMD) and the like.
2. Related Background Art
At the present, a display device employed for the HMD is exemplified such as a transparent type liquid crystal element, a reflection type liquid crystal element, or an EL (Electroluminescence) element. These types of elements are, as necessary pixels must be all built up in the elements, easy to have occurrence of a pixel defect and hard to be manufactured.
Further, a display device is proposed in U.S. Pat. No. 5,467,104, wherein an image is displayed and observed by employing a scanning device without using a two-dimensional display device such as the liquid crystal element and the EL element.
U.S. Pat. No. 5,467,104 discloses a scan type image display device that scans light beams assuming respective colors of Red, Green, and Blue in a horizontal direction and in a vertical direction, and directly forms the image on a retina via an optical system. An extremely high speed scan of the light beams is requested for the scan type image display device disclosed in U.S. Pat. No. 5,467,104, and therefore an extremely small-sized device is employed for a scanning element such as a mirror for scanning the light. Accordingly, the light beam to be scanned is quite narrow and therefore has an extremely small diameter (a diameter of an exit pupil) in a position of a pupil of an observer.
Methods for expanding the small diameter of the exit pupil are also proposed (U.S. Pat. Nos. 5,701,132 and 5,757,544).
On the other hand, a comparatively small-sized optical system using an eccentric free-form curved surface optical system is also proposed (Japanese Patent Application Laid-Open No. 2001-004955).
Known further is an image display device (Japanese Patent Application Laid-Open No. H11-095144) in which a scanning means is shared with optical systems corresponding to right and left eyes.
According to configurations disclosed in U.S. Pat. Nos. 5,701,132 and 5,757,544, an intermediate image is temporarily formed to expand the diameter of the exit pupil, and hence the device tends to be scaled up due to an elongated optical path.
Further, according to Japanese Patent Application Laid-Open No. H11-095144, two scanning devices for the horizontal direction and the vertical direction are employed, and consequently the configuration becomes complicated. In the construction disclosed in Japanese Patent Application Laid-Open No. H11-095144, when trying to obtain the HMD having a further wide field angle, the scanning device for the vertical direction becomes extremely elongate in the horizontal direction, resulting in the scale-up of the image observing apparatus.